1. Field of the Invention
This invention relates to electric lamps and has particular reference to an improved incandescent lamp of the bromine-cycle type.
2. Description of the Prior Art
Halogen incandescent lamps are per se well known in the art. A lamp of this type in which the regenerative-cycle is established and maintained by a small quantity of dosed elemental iodine (from 0.01 to 1 micromole per cm.sup.3 or ml. or bulb volume) is describe in U.S. Pat. No. 2,883,571 issued Apr. 21, 1959 to E. G. Fridrich et al. Another regenerative-cycle lamp that contains a fill gas and bromine or a bromine-releasing compound (such as hydrogen bromide) is disclosed in U.S. Pat. No. 3,091,718 issued May 28, 1963, to J. Shurgan. A halogen-cycle incandescent lamp that contains from 0.01 to 1.0 micromole per ml. of bulb volume of a mercury halogenide (such as mercury bromide or mercury iodide) and is filled with an inert gas such as argon, xenon, nitrogen, or a mixture of such gases, at a pressure of 600 to 650 torr is described in Czechoslovakian Patent No. 131,576 of Jiri Pavlata (published Sept. 15, 1968).
An incandescent projection type lamp in which a halogen-cycle is obtained by filling the lamp with predetermined amounts of mercury, bromine and an inert fill gas (such as nitrogen at a fill pressure of from 64 to 128 torr) is described in German Patent No. 1,928,442 of Bernhard Kopelman filed June 4, 1969 and opened to inspection on Dec. 11, 1969. Other types of incandescent lamps and a combination discharge-and-incandescent type lamp, etc. that contain various kinds and amounts of metal halides such as mercury iodide or mercury bromide are described in British Patent No. 1,105,291 and U.S. Pat. No. 3,497,754.
The dynamic "bulb-cleansing" phenomenon which occurs in halogen-cycle incandescent lamps and the resulting high luminous efficiency makes lamps of this type particularly useful for lighting TV studios and theaters where light of high-brightness and the proper color temperature is required. Bromine-cycle incandescent lamps designed and manufactured for use in such lightning applications in accordance with the prior art sometimes exhibit premature blackening of the envelope or fail to burn at their design efficiency, or for their design life (generally 400 hours or less). It would accordingly be desirable and very advantageous from a commercial standdpoint to correct these quality problems and provide reliable high-efficiency incandescent lamps for such lighting applications which would meet or exceed their performance ratings.